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Subject[tip:perf/core] perf/x86: Fix Intel shared extra MSR allocation
Commit-ID:  5a425294ee7d4ab5a374248e85838dfd450caf75
Gitweb: http://git.kernel.org/tip/5a425294ee7d4ab5a374248e85838dfd450caf75
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 5 Jun 2012 15:30:31 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 6 Jun 2012 17:22:26 +0200

perf/x86: Fix Intel shared extra MSR allocation

Zheng Yan reported that event group validation can wreck event state
when Intel extra_reg allocation changes event state.

Validation shouldn't change any persistent state. Cloning events in
validate_{event,group}() isn't really pretty either, so add a few
special cases to avoid modifying the event state.
The code is restructured to minimize the special case impact.

Reported-by: Zheng Yan <zheng.z.yan@linux.intel.com>
Acked-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1338903031.28282.175.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/cpu/perf_event.c | 1 +
arch/x86/kernel/cpu/perf_event.h | 1 +
arch/x86/kernel/cpu/perf_event_intel.c | 92 ++++++++++++++++++++++----------
3 files changed, 66 insertions(+), 28 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index e049d6d..cb60838 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1496,6 +1496,7 @@ static struct cpu_hw_events *allocate_fake_cpuc(void)
if (!cpuc->shared_regs)
goto error;
}
+ cpuc->is_fake = 1;
return cpuc;
error:
free_fake_cpuc(cpuc);
diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index 6638aaf..83794d8 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -117,6 +117,7 @@ struct cpu_hw_events {
struct perf_event *event_list[X86_PMC_IDX_MAX]; /* in enabled order */

unsigned int group_flag;
+ int is_fake;

/*
* Intel DebugStore bits
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 166546e..965baa2 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1119,27 +1119,33 @@ intel_bts_constraints(struct perf_event *event)
return NULL;
}

-static bool intel_try_alt_er(struct perf_event *event, int orig_idx)
+static int intel_alt_er(int idx)
{
if (!(x86_pmu.er_flags & ERF_HAS_RSP_1))
- return false;
+ return idx;

- if (event->hw.extra_reg.idx == EXTRA_REG_RSP_0) {
- event->hw.config &= ~INTEL_ARCH_EVENT_MASK;
- event->hw.config |= 0x01bb;
- event->hw.extra_reg.idx = EXTRA_REG_RSP_1;
- event->hw.extra_reg.reg = MSR_OFFCORE_RSP_1;
- } else if (event->hw.extra_reg.idx == EXTRA_REG_RSP_1) {
+ if (idx == EXTRA_REG_RSP_0)
+ return EXTRA_REG_RSP_1;
+
+ if (idx == EXTRA_REG_RSP_1)
+ return EXTRA_REG_RSP_0;
+
+ return idx;
+}
+
+static void intel_fixup_er(struct perf_event *event, int idx)
+{
+ event->hw.extra_reg.idx = idx;
+
+ if (idx == EXTRA_REG_RSP_0) {
event->hw.config &= ~INTEL_ARCH_EVENT_MASK;
event->hw.config |= 0x01b7;
- event->hw.extra_reg.idx = EXTRA_REG_RSP_0;
event->hw.extra_reg.reg = MSR_OFFCORE_RSP_0;
+ } else if (idx == EXTRA_REG_RSP_1) {
+ event->hw.config &= ~INTEL_ARCH_EVENT_MASK;
+ event->hw.config |= 0x01bb;
+ event->hw.extra_reg.reg = MSR_OFFCORE_RSP_1;
}
-
- if (event->hw.extra_reg.idx == orig_idx)
- return false;
-
- return true;
}

/*
@@ -1157,14 +1163,18 @@ __intel_shared_reg_get_constraints(struct cpu_hw_events *cpuc,
struct event_constraint *c = &emptyconstraint;
struct er_account *era;
unsigned long flags;
- int orig_idx = reg->idx;
+ int idx = reg->idx;

- /* already allocated shared msr */
- if (reg->alloc)
+ /*
+ * reg->alloc can be set due to existing state, so for fake cpuc we
+ * need to ignore this, otherwise we might fail to allocate proper fake
+ * state for this extra reg constraint. Also see the comment below.
+ */
+ if (reg->alloc && !cpuc->is_fake)
return NULL; /* call x86_get_event_constraint() */

again:
- era = &cpuc->shared_regs->regs[reg->idx];
+ era = &cpuc->shared_regs->regs[idx];
/*
* we use spin_lock_irqsave() to avoid lockdep issues when
* passing a fake cpuc
@@ -1173,6 +1183,29 @@ again:

if (!atomic_read(&era->ref) || era->config == reg->config) {

+ /*
+ * If its a fake cpuc -- as per validate_{group,event}() we
+ * shouldn't touch event state and we can avoid doing so
+ * since both will only call get_event_constraints() once
+ * on each event, this avoids the need for reg->alloc.
+ *
+ * Not doing the ER fixup will only result in era->reg being
+ * wrong, but since we won't actually try and program hardware
+ * this isn't a problem either.
+ */
+ if (!cpuc->is_fake) {
+ if (idx != reg->idx)
+ intel_fixup_er(event, idx);
+
+ /*
+ * x86_schedule_events() can call get_event_constraints()
+ * multiple times on events in the case of incremental
+ * scheduling(). reg->alloc ensures we only do the ER
+ * allocation once.
+ */
+ reg->alloc = 1;
+ }
+
/* lock in msr value */
era->config = reg->config;
era->reg = reg->reg;
@@ -1180,17 +1213,17 @@ again:
/* one more user */
atomic_inc(&era->ref);

- /* no need to reallocate during incremental event scheduling */
- reg->alloc = 1;
-
/*
* need to call x86_get_event_constraint()
* to check if associated event has constraints
*/
c = NULL;
- } else if (intel_try_alt_er(event, orig_idx)) {
- raw_spin_unlock_irqrestore(&era->lock, flags);
- goto again;
+ } else {
+ idx = intel_alt_er(idx);
+ if (idx != reg->idx) {
+ raw_spin_unlock_irqrestore(&era->lock, flags);
+ goto again;
+ }
}
raw_spin_unlock_irqrestore(&era->lock, flags);

@@ -1204,11 +1237,14 @@ __intel_shared_reg_put_constraints(struct cpu_hw_events *cpuc,
struct er_account *era;

/*
- * only put constraint if extra reg was actually
- * allocated. Also takes care of event which do
- * not use an extra shared reg
+ * Only put constraint if extra reg was actually allocated. Also takes
+ * care of event which do not use an extra shared reg.
+ *
+ * Also, if this is a fake cpuc we shouldn't touch any event state
+ * (reg->alloc) and we don't care about leaving inconsistent cpuc state
+ * either since it'll be thrown out.
*/
- if (!reg->alloc)
+ if (!reg->alloc || cpuc->is_fake)
return;

era = &cpuc->shared_regs->regs[reg->idx];

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